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Aptitude Topics

Number System

Number system is a fundamental topic in quantitative aptitude that deals with properties of numbers, divisibility rules, factors, multiples, and remainders. It is one of the most important topics for banking, SSC, CMAT, and placement exams.

Fundamental Principles

Natural Numbers

Counting numbers starting from 1 (1, 2, 3, ...).

Whole Numbers

All natural numbers including 0 (0, 1, 2, 3, ...).

Integers

Includes negative numbers, zero, and positive numbers (..., -2, -1, 0, 1, 2, ...).

Prime Numbers

Numbers greater than 1 having exactly two factors: 1 and itself (e.g., 2, 3, 5, 7).

Composite Numbers

Numbers having more than two factors (e.g., 4, 6, 8, 9).

Essential Formulation Tips

  • Learn divisibility rules from 2 to 11 for faster solving.
  • Memorize squares up to 30 and cubes up to 20.
  • Use factorization to simplify large numbers.
  • Always check for common factors in problems.

Shortcut Execution Techniques

  • Divisibility by 9: Sum of digits should be divisible by 9.
  • Divisibility by 11: Difference between sum of alternate digits should be multiple of 11.
  • Even numbers are divisible by 2; numbers ending in 0 or 5 are divisible by 5.
  • Use last digit concept to find unit digit quickly.

Contextual Inquiries (FAQs)

Q: What is the most important topic in number system for aptitude?

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Q: How to solve number system questions quickly?

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